git fetch-pack: add --diag-url

The main purpose is to trace the URL parser called by git_connect() in
connect.c

The main features of the parser can be listed as this:

- parse out host and path for URLs with a scheme (git:// file:// ssh://)
- parse host names embedded by [] correctly
- extract the port number, if present
- separate URLs like "file" (which are local)
  from URLs like "host:repo" which should use ssh

Add the new parameter "--diag-url" to "git fetch-pack", which prints
the value for protocol, host and path to stderr and exits.

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

connect.c

@@ -236,6 +236,20 @@ enum protocol {
 	PROTO_GIT
 };
 
+static const char *prot_name(enum protocol protocol)
+{
+	switch (protocol) {
+		case PROTO_LOCAL:
+			return "file";
+		case PROTO_SSH:
+			return "ssh";
+		case PROTO_GIT:
+			return "git";
+		default:
+			return "unkown protocol";
+	}
+}
+
 static enum protocol get_protocol(const char *name)
 {
 	if (!strcmp(name, "ssh"))
@@ -670,6 +684,20 @@ struct child_process *git_connect(int fd[2], const char *url,
 	signal(SIGCHLD, SIG_DFL);
 
 	protocol = parse_connect_url(url, &host, &port, &path);
+	if (flags & CONNECT_DIAG_URL) {
+		printf("Diag: url=%s\n", url ? url : "NULL");
+		printf("Diag: protocol=%s\n", prot_name(protocol));
+		printf("Diag: hostandport=%s", host ? host : "NULL");
+		if (port)
+			printf(":%s\n", port);
+		else
+			printf("\n");
+		printf("Diag: path=%s\n", path ? path : "NULL");
+		free(host);
+		free(port);
+		free(path);
+		return NULL;
+	}
 
 	if (protocol == PROTO_GIT) {
 		/* These underlying connection commands die() if they